Among the fastest growing trends named by brewers at the American Craft Beer Festival was barrel aging, so it’s no surprise that the world’s largest Irish whiskey producer, Jameson, is constantly approached by craft brewers looking for used barrels. Despite this, not once in Jameson’s 234 years of distilling whiskey had the company loaned their barrels to a U.S. company. Well, not until this year.

“We want to stay in control of everything that comes out of our barrels”, explained Dave Quinn, Jameson’s Master of Whiskey Science. But Quinn’s visit last week to Brooklyn marked an exception to this rule. Months before, the distiller had loaned ten bourbon barrels that had held Jameson for six years to Brooklyn native Kelly Taylor, Master Brewer and owner of KelSo Beer Co.. The barrels were for aging KelSo’s IPA. Due to limited availability, the beer that resulted was only on tap for one weekend at Dirck the Norseman, a brewpub in Greenpoint.

At the brewpub, in a small room adjoining the dining room, reporters and industry types stood around tables lined with beer and shot glasses, waiting to try the limited edition beer while Taylor and Quinn spoke about the collaboration, a short documentary on the project airing on a screen behind them. On every table, three separate coasters held a shot glass of Jameson Irish Whiskey sandwiched between two beer glasses. In the first was KelSo IPA; in the second was KelSo IPA that had been aged in Jameson barrels. The effect was obvious: drink the traditional IPA, taste what it was aged in, then drink the beautiful marriage of the two. Taylor chose to age an IPA (although they are usually best when drank freshly canned) because the “fruity and spicy and floral” notes evident in the whiskey would complement those same flavors in the beer. After a few months of aging, he dry-hopped the IPA before bottling in order to add back any bitter flavors lost — and to remove any off-flavors added — during the aging process. The result is a unique beer in a unique segment.

Barrel aging beer isn’t entirely new, but it’s also relatively unexplored. The process is riskier than traditional brewing methods for a number of reasons. For one, barrel aged beer is expensive to buy and expensive to make. The barrels cost money. The factory floor space — which sits unproductive, sometimes for upwards of a year — costs money. There are also high risks of infections, oxidation or just poor-tasting beer. On top of this, Taylor had only 10 barrels, meaning he didn’t have room for error. Without a doubt, the brewer labored particularly hard over this brew. You could almost say he coddled it.

Sadly, by the time you read this, all of the KelSo IPA aged in Jameson barrels will have been drunk. But here are some tasting notes for the curious or optimistic beer aficionado, anyways. The aged IPA had taken on a darker appearance from the Jameson barrel, tasted like the vanilla and nut flavors present in Jameson and had a light floral aroma that was overtaken by the alcoholic smell of whiskey, like sniffing the empty glass of a newly finished highball.

The tasting — beer over shot over beer — showed just how personalized barrel aging can be. As whiskey and beer are produced with similar ingredients, the Jameson barrel enhanced and layered the IPA without overpowering it. It was like previous IPAs had been in black and white, and with this one someone had filled in the colors. To get this effect, Taylor checked the aging beer often and ensured he kegged it at the right time, and for good reason. He said he could take the same base beer, age it in five or six different barrels and end up with five or six distinct beers. The Jameson collaboration was another proof positive of barrel aging’s ability to produce subtle but complex and layered flavors.

Taylor had taken a beer that isn’t traditionally aged and manipulated the process, crafting his own rules. This is part of the reasoning behind the current barrel age trend: you can have your cake and eat it too. You can drink strong ales that contain a nuanced flavor of your favorite red wine, or an IPA that reminds you of your highball glass. The barrels’ tastes sit in the background, adding complexity without flavors that are overtly “experimental”.

And this trend among craft brewers is guaranteed to continue, not only because craft beer grew 18 percent in 2013, but because a recent regulatory change, announced by the U.S. Alcohol and Tobacco Tax and Trade Bureau means brewers can now use more than 30 non-traditional ingredients in their beer without requiring government approval. This includes barrel aging, which previously had an approval process that took anywhere from weeks to months.

Maybe it was the undeniable, eventual dip of Jameson into barrel partnerships (along with many more producers) that motivated the KelSo & Jameson union. Quinn says it was a careful and controlled move into uncharted territory, with a trusted brewer from the city where Jameson made its start in the American market. The reasons don’t matter; the box has been opened. Look out for more beers attempting to cash in on the brand name of other great alcohol providers (because great alcohol begets great barrels for aging), and don’t be afraid to shell out the extra money. It certainly beats fruit beers.